From 82b6ae7ab52df111b27c34c81f1f61bd3837a750 Mon Sep 17 00:00:00 2001
From: Luka Jacobowitz <luka.jacobowitz@codecentric.de>
Date: Mon, 21 Aug 2017 19:36:08 +0200
Subject: [PATCH] Initial version of Parallel

---
 core/src/main/scala/cats/Parallel.scala       | 60 +++++++++++++++++++
 .../src/main/scala/cats/syntax/parallel.scala | 32 ++++++++++
 2 files changed, 92 insertions(+)
 create mode 100644 core/src/main/scala/cats/Parallel.scala
 create mode 100644 core/src/main/scala/cats/syntax/parallel.scala

diff --git a/core/src/main/scala/cats/Parallel.scala b/core/src/main/scala/cats/Parallel.scala
new file mode 100644
index 00000000000..da80bacaeb4
--- /dev/null
+++ b/core/src/main/scala/cats/Parallel.scala
@@ -0,0 +1,60 @@
+package cats
+
+trait Parallel[M[_], F[_]] {
+  def applicative: Applicative[F]
+  def sequential(implicit M: Monad[M]): F ~> M
+  def parallel(implicit M: Monad[M]): M ~> F
+}
+
+object Parallel {
+  def parSequence[T[_]: Traverse, M[_]: Monad, F[_], A]
+  (tma: T[M[A]])(implicit P: Parallel[M, F]): M[T[A]] = {
+    implicit val F = P.applicative
+    val fta: F[T[A]] = Traverse[T].traverse(tma)(P.parallel.apply)
+    P.sequential.apply(fta)
+  }
+
+  def parTraverse[T[_]: Traverse, M[_]: Monad, F[_], A, B]
+  (ta: T[A])(f: A => M[B])(implicit P: Parallel[M, F]): M[T[B]] = {
+    implicit val F = P.applicative
+    val gtb: F[T[B]] = Traverse[T].traverse(ta)(f andThen P.parallel.apply)
+    P.sequential.apply(gtb)
+  }
+
+  def parSequence_[T[_]: Foldable, M[_]: Monad, F[_], A]
+  (tma: T[M[A]])(implicit P: Parallel[M, F]): M[Unit] = {
+    implicit val F = P.applicative
+    val fu: F[Unit] = Foldable[T].traverse_(tma)(P.parallel.apply)
+    P.sequential.apply(fu)
+  }
+
+  def parTraverse_[T[_]: Foldable, M[_]: Monad, F[_], A, B]
+  (ta: T[A])(f: A => M[B])(implicit P: Parallel[M, F]): M[Unit] = {
+    implicit val F = P.applicative
+    val gtb: F[Unit] = Foldable[T].traverse_(ta)(f andThen P.parallel.apply)
+    P.sequential.apply(gtb)
+  }
+
+  def parAp[M[_]: Monad, F[_], A, B](mf: M[A => B])
+                                    (ma: M[A])
+                                    (implicit P: Parallel[M, F]): M[B] = {
+    implicit val F = P.applicative
+    val fb = Applicative[F].ap(P.parallel.apply(mf))(P.parallel.apply(ma))
+    P.sequential.apply(fb)
+  }
+
+  def parProduct[M[_]: Monad, F[_], A, B](ma: M[A], mb: M[B])
+                                         (implicit P: Parallel[M, F]): M[(A, B)] =
+    parAp(Monad[M].map(ma)(a => (b: B) => (a, b)))(mb)
+
+  def parAp2[M[_]: Monad, F[_], A, B, Z](ff: M[(A, B) => Z])
+                                        (ma: M[A], mb: M[B])
+                                        (implicit P: Parallel[M, F]): M[Z] =
+    Monad[M].map(parProduct(ma, parProduct(mb, ff))) { case (a, (b, f)) => f(a, b) }
+
+  def parMap2[M[_]: Monad, F[_], A, B, C](ma: M[A], mb: M[B])
+                                         (f: (A, B) => C)
+                                         (implicit P: Parallel[M, F]): M[C] = {
+    Monad[M].map(parProduct(ma, mb)) { case (a, b) => f(a, b) }
+  }
+}
diff --git a/core/src/main/scala/cats/syntax/parallel.scala b/core/src/main/scala/cats/syntax/parallel.scala
new file mode 100644
index 00000000000..470e56b0d28
--- /dev/null
+++ b/core/src/main/scala/cats/syntax/parallel.scala
@@ -0,0 +1,32 @@
+package cats.syntax
+
+import cats.{Monad, Parallel, Traverse}
+
+trait parallel {
+  implicit final def catsSyntaxParallelTraverse[T[_]: Traverse, A]
+  (ta: T[A]): ParallelTraversableOps[T, A] = new ParallelTraversableOps[T, A] {
+    override def self = ta
+
+    override val typeClassInstance: Traverse[T] = T
+  }
+}
+
+
+
+
+trait ParallelTraversableOps[T[_], A] {
+
+  val typeClassInstance : cats.Traverse[T]
+  def self : T[A]
+
+  implicit val T = typeClassInstance
+
+  def parTraverse[M[_]: Monad, F[_], B]
+  (f: A => M[B])(implicit P: Parallel[M, F]): M[T[B]] =
+    Parallel.parTraverse(self)(f)
+
+  def parSequence[M[_]: Monad, F[_], B](implicit ev: A <:< M[B], P: Parallel[M, F]): M[T[B]] =
+    Parallel.parSequence(self.asInstanceOf[T[M[B]]])
+
+
+}